The present invention concerns a method for the mixing of liquid or gas into pulp stock and an apparatus for carrying out the method.
The flow-technical properties of a pulp stock of low consistency, i.e. of a stock whose consistency is lower than 5%, correspond to a Newtonian fluid, and such a stock can be pumped by means of centrifugal pumps and propeller pumps. Mixing of liquid or gas into stock of low consistency does not cause particular difficulties. For the pumping of pulp stock of medium consistency, i.e. of a stock whose consistency is 8% to 18%, displacement pumps have been used traditionally. However, it has been noticed that a stock of medium consistency becomes pumpable when it is fluidized, i.e. subjected to a sufficiently rapid shear. A centrifugal pump based on fluidization is described, e.g., in the U.S. Pat. No. 4,435,122. Mixing of liquid or gas into pulp stock in the range of medium consistency is more difficult than in the range of low consistency, mainly because there is little free liquid between the fibres.